Concrete masonry units are available in a wide range of sizes and shapes, and are used for a variety of applications ranging from concrete blocks and bricks to segmental retaining wall blocks (the latter are sometimes called xe2x80x9cSRWxe2x80x9d blocks).
Depending on the intended end-use application of the concrete masonry units being produced, the surface appearance of the units may be important and the marketplace has come to expect various decorative or cosmetic surface finishes for many masonry units. Such surface finishes include those commonly described as broken or split, striped, striated, simulated broken, and smooth (alone or in combination with one of the other surface finishes). One such surface finish is a texture that resembles the appearance of a xe2x80x9csplitxe2x80x9d rock. A xe2x80x9csplitxe2x80x9d surface finish on a concrete masonry unit may be achieved by mechanically splitting away a portion of a face of the masonry unit. This is typically achieved with a mechanical splitting blade similar to a guillotine and the splitting is performed on the masonry units after they have been cured or hardened. To avoid waste, this is often done by first forming the masonry units as xe2x80x9cSiamesexe2x80x9d twins and then splitting them apart. The resulting fractured surface on the front face of both blocks is generally thought to be pleasing to look at and is sought after.
The mechanical splitting of masonry units is an added cost of processing since one must invest in the splitting equipment, and transport the masonry units from their place of curing to the splitter, and then to a suitable collection station for palletizing or the like. When the applicable capital, labor and other costs (e.g. utilities and floor space) are added together, this added cost is significant. This cost provides a substantial incentive to develop new methods of roughening the surface of masonry units to create a desirable surface finish without the need to mechanically split the masonry units. Although some approaches have involved processing steps to be performed on the green or uncured masonry units immediately after they are discharged from the mold, the most common approach has been to modify the mold in some fashion so that a roughened surface is produced on the concrete masonry units as they are ejected from the mold (i.e. the masonry units are roughened in the mold cavity).
For example, U.S. Pat. No. 3,940,229 describes a mold for making concrete masonry units with a roughened texture on at least one face. The mold has a wall with a lip on the lower edge of the wall, that projects inwardly into the mold cavity. The lip is rectangular in profile, and it may be smooth or it may be serrated to provide sawtooth-like projections. As the shaped but uncured concrete masonry unit is forced out of the bottom of the mold, the patent says that the protruding lip produces a scraping or tearing action on the adjacent face of the concrete masonry unit so as to roughen the surface of the masonry unit. Although a small amount of fill material will loosely rest on or adhere to the mold wall above the lip after use, the mold of U.S. Pat. No. 3,940,229 is self-cleaning since the small amount of material that remains loosely adhered to the mold wall after the mold is stripped is knocked clear of the wall when the next machine pallet is placed against the mold bottom and the mold is vibrated. Experiments with this type of mold demonstrate that it produces a roughened surface on the concrete unit, but that the face sometimes has a slight xe2x80x9cshingledxe2x80x9d appearance. Further, the lip is relatively small, and wear is a problem with the passage of time due to the abrasive nature of the moldable fill material from which the concrete masonry unit is formed. The lip is also susceptible to damage if the head of the block machine is not properly aligned. Replacing the lip is time consuming. Sometimes a new lip is welded to the mold and at other times a new mold wall is made.
A modified form of the lip design of U.S. Pat. No. 3,940,229 has been developed and that modified lip design is the subject of U.S. Pat. No. 6,209,848 entitled xe2x80x9cMOLD FOR PRODUCING MASONRY BLOCK WITH ROUGHENED SURFACExe2x80x9d. According to that patent (which is incorporated herein by reference), a satisfactory roughened surface is produced by forming grooves in a wedge shaped lower lip with the grooves at an angle to the direction of travel that the material moves through the mold. Masonry units made with this improved mold seem to have less shingling than units made with a solid or serrated lower lip. The mold remains self-cleaning. However, the grooves in the lower lip are subject to the same wear and damage as the lower lip of U.S. Pat. No. 3,940,229.
U.S. Pat. Nos. 5,078,940 and 5,217,630 describe a somewhat different type of mold for making concrete masonry units with a roughened surface. Although the molds described in these patents also employ a protruding lip on the lower edge of at least one wall of the mold, the lip is wedge-shaped in profile. In addition, the mold includes a plurality of projections above the lip on the same wall and these multiple projections also intrude into the mold cavity. In addition, an optional mesh extends upwardly from the lip generally close to and parallel to the wall and associated projections. In use, concrete fill material is introduced into the mold and compressed to a size slightly xe2x80x9coversizexe2x80x9d of the desired masonry unit. The projections and the mesh are designed to retain a meaningful portion of the concrete fill material in place against the wall of the mold as the formed concrete masonry unit is forced out of the bottom of the mold. As described in these patents, the concrete fill material held against the mold wall by the projections and the mesh is sheared from the concrete masonry unit that is being forced out of the mold, thus forming a roughened surface on the concrete masonry unit as it is ejected from the mold. These patents teach that the mold is then re-used one or more times to make additional masonry units and the concrete fill material retained in the mold remains in place and reportedly assists in roughening the surface of the masonry units that are successively formed in the same mold. Molds of this type are not self-cleaning, but are designed to retain fill material on the projections and against a wall of the mold during successive machine cycles. It is believed that molds of this design, although without the mesh, have been commercialized under the trademark xe2x80x9cSoftsplitxe2x80x9d. Others familiar with the use of this process on a commercial scale have reported that the process must occasionally be interrupted to clean out the fill material that agglomerates around the projections since the fill material eventually becomes too hard for this process to be effective. This is not necessarily an easy cleaning process. It depends upon how accessible the mold face is to the machine operator. In many of the commonly used concrete block machines, the mold faces are relatively difficult to get at, and safety dictates that precautions such as machine lockouts and the like be used when the cleaning process is undertaken. The cleaning process is not easy, and is costly since production is interrupted for cleaning to take place.
U.S. Pat. No. 5,879,603 describes an improvement to the ""229 style mold. The ""603 patent describes a mold with a wedge-shaped lower lip and an upper lip spaced apart from the lower lip by the distance defining the height of the concrete unit to be produced. Both lips protrude into the mold cavity. The mold acts in a similar fashion to the molds of U.S. Pat. No. 3,940,229, but produces less xe2x80x9cshinglingxe2x80x9d effect on the roughened face, and is also self-cleaning in the same fashion, i.e. the concrete fill material that loosely adheres to the lower lip and to the mold wall above the lower lip is knocked off the wall when the next pallet is brought into place beneath the mold and the mold is vibrated.
U.S. Pat. No. 6,113,379 describes another style of mold for roughening the surface of a masonry unit as it is ejected from the mold. This mold incorporates an expanded metal grate, which spans a single mold cavity, dividing it into to sub-cavities which are in communication with each other. Fill material is introduced into the mold cavity, and the fill material is compressed. During this time, the fill material passes through the grate and a single molded article is made which occupies both sub-cavities. As the single molded article is ejected from the mold, the grate divides the molded unit into two masonry units, which are both ejected from the mold. During the process of being ejected from the mold, the faces of the masonry units, which were adjacent the expanded metal grate, are roughened. Experiments have shown this mold to be self cleaning, and any fill material that is loosely attached to or suspended on the grate or delicately balanced in the grate openings is readily dislodged and drops to the pallet when the mold is vibrated as part of the next machine cycle.
At times, it is desired to produce a more modest or fine roughening of a masonry unit than is typically produced when mechanically splitting a block. Unfortunately, the molds used to produce pronounced roughening are often unsuited for the more modest roughening. If they are scaled down to produce more moderate roughening, they often have more delicate features that lack the desired strength and wearability.
Modest roughening of one or more surfaces of a masonry unit such as a brick or block is useful not only as the only surface finish, but is useful in combination with mechanical splitting where the modest roughening can be performed on surfaces of the block which are not to be mechanically split, but which may be visible to the observer when the products are used, for example, to create a retaining wall. By roughening the surfaces immediately adjacent to the mechanically split surface(s), light striking the adjacent surfaces is scattered and the reflections associated with smooth reflective surfaces are avoided.
The present invention is a still different type of mold, which is easy to fabricate and which is durable and self-cleaning. This new mold is especially suited for creating fine or modest roughened surfaces on concrete masonry units. These moderately roughened surfaces are suitable for use as the decorative face(s) on concrete products such as bricks and blocks.
The desired result of producing a modest or fine roughened surface on a masonry unit can be performed in a mold without using protruding lips or wall projections or grates, although such features could be used to supplement the action described herein. For simplicity, such features, especially the more complicated ones, will usually be avoided.
According to the present invention, one or more shallow channels or grooves are cut or otherwise formed in the face of the mold wall or walls or other generally vertical surface(s) within the mold from which it is desired to produce a roughened surface on a masonry unit. These channels are not parallel to the direction in which the mold is stripped, but rather are perpendicular to or oblique to the direction of stripping. In its simplest form, a single and generally horizontal channel (i.e. a channel perpendicular to the direction of stripping) will be cut across the face of a wall of the mold, generally near the bottom of the wall (e.g. less than about 0.5 inches from the bottom of the mold and usually less than about 0.1 inch from the bottom of the mold) adjacent the point where the masonry unit will be ejected from the mold. The depth and height of the channel will he selected to provide the optimum or desired surface roughness for the intended application, taking into consideration the mix design for the fill material, which includes aggregate size and distribution, amount and type of cement, and amount of water. Although the channel can be rectangular in cross section, other shapes can be used such as semi-circular or v-shaped or ear-shaped, and multiple channels can be used. These multiple channels can be at the same or different heights on the mold wall. The channels may be generally parallel to the bottom of the mold or they may be skewed or even non-linear such as serpentine. Criss-cross patterns can be used. The channels may extend partly or entirely across the face of the mold.
Molds of the present design are self-cleaning since the channels are shallow and any loose fill material lying in the channels is readily shaken loose by the vibration of the mold. Further, the rapid wear problems associated with thin protruding lower lips like those used in U.S. Pat. No. 3,940,229 are minimized, and the potential for damage to protruding lips such as those of U.S. Pat. No. 3,940,229 due to head misalignment are minimized if not eliminated.
Further, these same channel features can be provided on other generally vertical shaping surfaces of the mold, and these other surfaces need not be planar although it is preferred to use the channels of the present invention as a feature on one or more of the generally planar vertical walls of the mold.
FIG. 1 is a perspective view of a mold having multiple cavities for producing concrete masonry units.
FIG. 2 is a front view of the front wall of a mold in which multiple shallow diagonal grooves or channels have been cut in the front wall at an angle to the horizontal of about 30 degrees.
FIG. 3 is a sectional view of the mold shown in FIG. 2 taken at line 3xe2x80x943 to show the cross section of the grooves.
FIG. 4 is a front view of the front wall of a mold in which a single horizontal groove or channel has been cut in the front wall close to the bottom of the wall.
FIG. 5 is a sectional view of the mold shown in FIG. 4 taken at line 5xe2x80x945 to show the cross section of the groove.
FIG. 6 is a front view of the front wall of a mold in which multiple, shallow, diagonal grooves or channels have been cut in the front wall at an angle to the horizontal of about 45 degrees to provide a xe2x80x9ccriss-crossxe2x80x9d pattern.
FIG. 7 is a sectional view of the mold shown in FIG. 6 taken at line 7xe2x80x947, to show the cross section of the grooves.
FIG. 8 is a front view of the front wall of a mold in which multiple horizontal grooves or channels have been cut in the front wall, extending from near the bottom of the mold wall to near the top of the mold wall.
FIG. 9 is a sectional view of the mold shown in FIG. 8 taken at line 9xe2x80x949, to show the cross section of the grooves.
FIG. 10 is a front view of the front wall of a mold in which a single horizontal groove or channel has been cut in the front wall close to the bottom of the front wall.
FIG. 11 is a sectional view of the mold shown in FIG. 10 taken at line 11xe2x80x9411, to show the cross section of the groove.
FIG. 12 is a front view of the front wall of a mold in which multiple diagonal grooves or channels have been cut in the front wall at an angle of 45 degrees from the horizontal.
FIG. 13 is a sectional view of the mold shown in FIG. 12 taken at line 13xe2x80x9413, to show the cross section of the groove.
FIG. 14 is a front view of a wall of a mold in which a serpentine groove or channel has been cut.